Moderate energy restriction increases bone resorption in obese postmenopausal women

Background: Weight reduction reduces bone mineral density (BMD) and increas es the risk of osteoporosis. Objective: We investigated whether bone is mobilized in postmenopausal wome n during energy restriction and whether hormones regulate bone turnover and mass. Design: Twenty-seven obese postmenopausal women with a mean (+/-SD) age of 55.9 +/- 7.9 y and body mass index (in kg/m(2)) of 33.0 +/- 3.8 completed t he 6-mo study. Fourteen women followed a moderate energy-restricted diet (W L group) and 13 control subjects maintained their body weight (WM group). B ody weight, bone turnover markers, serum parathyroid hormone (PTH), and die tary intake were measured throughout the study. Total-body BMD, sex hormone binding globulin, leptin, acid estrone were measured at baseline and at we ek 25. Results: In the WL group, body weight decreased by 10.2 +/- 5.5% (P < 0.001 ), body fat mass decreased by 18.7 +/- 11.3% (P < 0.001), and total-body BM D decreased by 1.2 +/- 1.2%; these changes were significantly different fro m those in the WM group (P < 0.05). Serial measurements showed chronically elevated rates of bone resorption and formation during energy restriction t hat were greater than in the WM group (P < 0.05). Serum sex hormone binding globulin increased and leptin decreased with weight loss (P < 0.05). Serum PTH tended to increase in the WL group but not in the WM group (P < 0.06). The reduction in fat mass with weight loss was directly associated with a decrease in serum estrone (P < 0.01, R-2 = 0.50). Conclusions: Moderate energy restriction increases bone turnover in obese p ostmenopausal women and may be regulated in part by alterations in serum PT H and estrone.